Printed circuit boards allow for reliable and cost-effective production of electronic devices. A common technique for populating printed circuit boards with components, for example surface-mount components, involves applying solder paste to desired areas of a printed circuit board through a specially configured stencil. The components are then pressed into the solder paste, and the populated circuit board is passed through an oven to reflow the solder paste.
Some printed circuit assemblies call for a mixture of different sized components, such as small or fine-pitched component leads alongside components with large leads or a large footing to be attached to the circuit board. This situation arises, for example, when a radiofrequency (RF) shield is used to isolate other electronic components. The RF shield is the large component, while the other electronics are configured to be placed on the circuit board underneath the RF shield and are hence smaller.
However, providing an appropriate amount of accurately placed solder paste for both large and small components presents a challenge. For example, a thinner stencil is generally conducive for applying solder paste for smaller components, whereas a thicker stencil is generally conducive for applying solder paste for larger components. Previous solutions to this problem include using multiple stencils with multiple rounds of solder paste application, and using specialized “step” stencils having variable thickness. This can introduce cost and complexity into the manufacturing process, and can reduce quality yields in the finished product.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.